1. Temperature, Hardness and Toughness

2. Temperature Effects on Material Properties
Temperature changes and extremes affect the value of many engineering properties
yield, modulus, toughness, corrosion resistance, creep, relaxation, viscosity, shrinkage, solubility…..

3. Temp Effect on Tensile Strength

4. Temp Effect on Other Properties

5. Thermal Expansion
Elevated Temperatures excite the electrons at the atomic level of any material
The excited atoms can more easily move to a lower energy state and change orientation of atomic planes
This leads to dimensional changes in most materials
There are exceptions, e.g. InVar, Ni-Cr alloy with a very low energy state that is not easily altered.

6. Temperature vs. Expansion
t is the coefficient of thermal expansion.
t is typically a constant.

7. Surface Properties Hardness Impact Energy Scratch hardness
Surface Hardness
Impact Energy

8. Hardness - Moh’s Scale
Moh scale is a surface scratch resistant scale based on minerals
1 - Talc
2 - Gypsum
3 - Calcite (CaCO3)
4 - Flourite
5 - Apatite
6 - Orthoclase (Feldspar)
7 - Quartz
8 - Topaz
9 - Corundum (or sapphire)
10 - Diamond
The Moh scale is a test of scratch resistance, based on empirical relationships developed in mineralogy.

9. Surface Hardness
Surface hardness is quantified by determining the energy necessary to cause localized plastic deformation.
A specific energy is imparted on a surface of a material and the amount of plastic deformation is quantified in most hardness procedures.
Based on theory of plasticity.

10. Types of hardness tests
Brinell ball original hardness test
Rockwell , rounded cone most common, (ASTM E18)
Hardness values depends on: Method used, Shape of indenter - spherical, pyramidal, diamond shape, etc., Dimensions of indenter, Magnitude of load placed on indenter
However, the hardness energy can be converted from one method to another.
Vickers pyramid, first micro-hardness test, similar to Brinell, used for thin specimens
Knoop diamond pyramid more refined micro-hardness
Note: P = Applied load in all tests
120°

11. Use of hardness Surface hardness of heat treated metals
Quality control of heat treatment process
Correlated with other properties
Yield strength
“Brittleness”

12. Impact tests Charpy V-notch - Measure energy required to
rupture specimen
Izod V-notch
- Same as Charpy but
different specimen

13. Use of impact resistance
Quantify resistance to dynamic impacts and crack sensitivity
Quantify the “transition temperature” of an alloy
(ductile – brittle behavior)
Impact Energy, Joules
Temperature
Ductile
Brittle